An alternating current leakage current fault diagnosis method

Abstract

The application discloses an alternating current leakage current fault diagnosis method, comprising the following steps: a vehicle power distribution box samples leakage currents of a fire line and a zero line of an alternating current electrical equipment to a shell through a zero sequence current transformer, determines single sampling values and sampling average values of the leakage currents, and judges stability of the sampling average values; safety protection currents and corresponding durations of instantaneous leakage currents and cumulative leakage currents are set; cumulative leakage current detection logic is executed by using the single sampling values of the leakage currents, the safety protection currents of the cumulative leakage currents and the corresponding durations, so as to judge whether it is a cumulative leakage current fault; a difference between the single sampling values of the leakage currents and sampling average values of a previous cycle, the safety protection currents of the instantaneous leakage currents and the corresponding durations are used to execute instantaneous leakage current detection logic, so as to judge whether it is an instantaneous leakage current fault; when the cumulative leakage current fault or the instantaneous leakage current fault is detected, the vehicle power distribution box automatically cuts off power input, and simultaneously performs alarming.

Description

Technical Field

[0001] This invention relates to the field of power electronics, specifically to a method for diagnosing AC leakage current faults. Background Technology

[0002] Conventional vehicle 380V AC power distribution designs typically employ a TN-S system, completely separating the protective neutral and neutral wires. 380V AC mains power is input to the vehicle's distribution box via a 4-wire system (3 live wires, 1 neutral wire), which then distributes the AC power to the electrical equipment according to instructions. The outer shielding layer of the cables, the mounting brackets for the electrical equipment, and the grounding copper rod are connected together through the vehicle body shell, with the grounding copper rod directly inserted into the ground. A high-sensitivity 30mA (operating time ≤0.1s) instantaneous electronic residual current device (RCD) is added to the input terminal of the vehicle's distribution box. When an insulation fault occurs in the equipment (cable), the RCD trips, preventing electric shock to the operator.

[0003] This design method has several drawbacks: 1. The sensitivity and reliability of electronic residual current devices (RCDs) are significantly affected by environmental factors such as temperature, humidity, and dust. Furthermore, the circuit breaker itself uses a mechanical tripping mechanism, which has high sensitivity but low reliability, making it prone to malfunctions over prolonged use. 2. Electrical equipment typically incorporates power filters and feedthrough filters at the power input. The common-mode capacitor in these filters forms a loop with the casing, generating leakage current. Power devices, when designed for heat dissipation, are placed close to the heat sink or equipment casing, creating distributed capacitance. This distributed capacitance, forming a loop with the casing, also generates leakage current. RCDs are highly sensitive to even small leakage currents, and the inherent leakage current of these devices may cause malfunctions. 3. RCDs only provide protection when the total leakage current exceeds 30mA. They cannot determine the specific value of the actual leakage current or detect the leakage current generated by individual devices, hindering fault diagnosis and troubleshooting. 4. RCDs are off-the-shelf products; the 30mA safety protection threshold and 0.1s operating time cannot be changed, preventing adjustments based on the actual conditions of the electrical equipment and load, resulting in poor flexibility.

[0004] There is a need to design a new method for diagnosing AC leakage current, which can effectively detect leakage current caused by equipment insulation faults or cable sheath damage, and prevent leakage protection from malfunctioning due to the inherent leakage current of electrical equipment, thus ensuring the normal operation of the system. Summary of the Invention

[0005] The purpose of this invention is to provide an AC leakage current fault diagnosis method to solve the problems of low reliability, poor flexibility, and easy malfunction of traditional leakage current protection methods.

[0006] To achieve the above objectives, the present invention employs the following technical solution: An AC leakage current fault diagnosis method includes: The vehicle-mounted electrical distribution box samples the leakage current of the live and neutral wires of the AC electrical equipment to the casing through a zero-sequence current transformer, determines the single sample value and the average value of the leakage current, and judges the stability of the average value; and sets the safety protection current and corresponding duration for instantaneous leakage current and cumulative leakage current. The cumulative leakage current detection logic is executed using the single sample value of the leakage current, the cumulative leakage current safety protection current, and the corresponding duration to determine whether it is a cumulative leakage current fault. The difference between a single sample value of the leakage current and the average value of the previous cycle, along with the instantaneous leakage current safety protection current and the corresponding duration, is used to execute instantaneous leakage current detection logic to determine whether it is an instantaneous leakage current fault. When a cumulative leakage current fault or a transient leakage current fault is detected, the vehicle's electrical distribution box automatically cuts off the power input and issues an alarm.

[0007] Furthermore, the vehicle is designed with a dedicated grounding copper plate. The mounting rack or cabinet for AC electrical equipment is connected to the vehicle's dedicated grounding wire. The vehicle's dedicated grounding wire is connected to the grounding copper rod on the grounding copper plate, and the grounding copper rod is inserted into the ground. This allows the leakage current to flow into the ground quickly in the event of a leakage current protection mechanism failure.

[0008] Furthermore, the determination of the single sample value and the average sample value of the leakage current specifically involves: The leakage current sampling module of the vehicle power distribution box reads the leakage current value collected by the zero-sequence current transformer once every T1 time, and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value. After the sampling module continuously reads the single sample value N1 times in one cycle, it calculates the average value of the current N1 single sample values ​​and compares it with the N1 single sample values. If the difference is less than or equal to the sampling value threshold, the average value is recorded; if there is a difference greater than the sampling value threshold, the average value is not recorded.

[0009] Furthermore, T1 is 10ms, N1 is 32 times, and the sampling threshold is 4mA.

[0010] Furthermore, a stable sampled average value is the inherent leakage current generated during the design of electrical equipment, excluding leakage current caused by equipment insulation faults; by reducing the number and capacity of common-mode capacitors in electrical equipment, the distributed capacitance of the system is reduced, thereby reducing the inherent leakage current.

[0011] Furthermore, the cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms; the instantaneous leakage current safety protection current is set to 25mA, and the instantaneous leakage current safety protection duration is set to 150ms.

[0012] Furthermore, the cumulative leakage current detection logic is as follows: When the single sample value of the current leakage current is detected to be greater than the cumulative leakage current safety protection current, the filtering timer starts. During the filtering timer, the single sample value is continuously sampled in the form of a sliding window. If each single sample value is greater than the cumulative leakage current safety protection current during the filtering timer until the cumulative leakage current safety protection duration, it is determined to be a cumulative leakage current fault and the output is cut off.

[0013] Furthermore, the instantaneous leakage current detection logic is as follows: When the difference ΔI between the current single-sample value of leakage current and the average value of the previous cycle is greater than the instantaneous leakage current safety protection current, filtering timing begins. During the filtering timing process, single-sample values ​​are continuously acquired in the form of a sliding window, and the average value of each cycle and the difference ΔI between them are calculated. If, during the filtering timing process until the instantaneous leakage current safety protection time is reached, each difference ΔI is greater than the instantaneous leakage current safety protection current, it is recorded as a fault sampling result. Single-sample values ​​are acquired again and the above process is repeated. If three consecutive sampling results are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off simultaneously. Furthermore, when calculating the difference ΔI for the first time, the average value of the samples from the previous period is calculated as 0.

[0014] A terminal device includes a processor, a memory, and a computer program stored in the memory; when the processor executes the computer program, it implements the AC leakage current fault diagnosis method.

[0015] A computer-readable storage medium storing a computer program; when the computer program is executed by a processor, it implements the AC leakage current fault diagnosis method.

[0016] Compared with the prior art, the present invention has the following technical features: This invention is novel in design, highly reliable, and flexible in use. It has already been implemented in a project. The results show that this method can detect leakage current caused by equipment or cable insulation faults in real time, effectively preventing false alarms caused by the high sensitivity of traditional methods, and meeting the application requirements. Attached Figure Description

[0017] Figure 1 The logic flow for cumulative leakage current detection; Figure 2This is the logic flow for instantaneous leakage current detection. Detailed Implementation

[0018] This invention provides an AC leakage current fault diagnosis method applicable to vehicle TN-S systems, comprising: the vehicle power distribution box sampling the leakage current of the live wire and neutral wire of the 380V AC electrical equipment to the casing (ground) through a zero-sequence current transformer, determining the single sampling value and the average value of the leakage current, and determining the stability of the average value; and setting the safety protection current and corresponding duration of the instantaneous leakage current and the cumulative leakage current through the display screen interface of the vehicle power distribution box. The cumulative leakage current detection logic is performed by using the single sample value of leakage current, the cumulative leakage current safety protection current, and the corresponding duration to determine whether there is a cumulative leakage current fault. The difference between a single sample value of the leakage current and the average value of the previous cycle, along with the instantaneous leakage current safety protection current and the corresponding duration, is used to perform instantaneous leakage current detection logic to determine whether it is an instantaneous leakage current fault. When a cumulative leakage current fault or a momentary leakage current fault is detected, the vehicle's electrical distribution box automatically cuts off the power input and sounds a buzzer alarm to achieve the purpose of leakage protection. The vehicle is designed with a dedicated grounding copper plate. The mounting frame (or cabinet) of the AC electrical equipment is connected to the vehicle's dedicated grounding wire by bolts. The vehicle's dedicated grounding wire and the grounding copper rod are reliably connected to the grounding copper plate by bolts. The grounding copper rod is inserted into the ground. In the event of leakage current protection failure, the leakage current can quickly flow into the ground, avoiding the risk of electric shock to personnel and effectively protecting the personal safety of operators.

[0019] Figure 1 The cumulative leakage current detection logic flow is shown. Figure 2 The instantaneous leakage current detection logic flow is shown; two leakage current detection logic flows are performed simultaneously. When one of them meets the leakage current fault condition, it is determined to be a leakage current fault, and the AC input is cut off.

[0020] Depend on Figure 1 , Figure 2 It can be seen that the leakage current detection logic flow consists of the following parts: (1) Leakage current sampling.

[0021] The leakage current sampling module of the vehicle power distribution box reads the leakage current value collected by the zero-sequence current transformer every 10ms and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value. After the sampling module continuously reads 32 single-sample values ​​for one cycle (a total of 320ms), it calculates the average value of the current 32 single-sample values ​​and compares it with the 32 single-sample values. If the difference is less than or equal to 4mA (the leakage current is considered stable within 320ms), the average value is recorded. If the difference is greater than 4mA (the leakage current is considered unstable within 320ms), the average value is not recorded. The resolution of both the single-sample value and the average value of the leakage current is 0.1mA. A stable average sampling value is the inherent leakage current generated during the design of electrical equipment, excluding leakage current caused by equipment (or cable) insulation faults. The inherent leakage current can be reduced by decreasing the number and capacity of the common-mode capacitor of the electrical equipment and reducing the distributed capacitance of the system. However, it is difficult to make changes due to its connection with product design. When the average sampling value reaches or even exceeds the safe protection current of the cumulative leakage current, it must be changed.

[0022] (2) Leakage current safety protection threshold setting. According to the band division diagram of the effects of electric current on the human body recommended in GB / T 13870.1 "Effects of Electric Current on Humans and Livestock - Part 1: General Part", a current passing through the human body of less than 50mA with a corresponding duration of less than 100ms will not cause harm. A current passing through the human body of less than 50mA with a corresponding duration of less than 1s generally will not cause ventricular fibrillation. A current passing through the human body of less than 100mA with a corresponding duration of less than 500ms generally will also not cause ventricular fibrillation. However, when the current passing through the human body continues to increase and the duration is very short (e.g., 500mA for 100ms), there is still a risk of inducing ventricular fibrillation.

[0023] The design takes into account actual operating conditions and the leakage current characteristics of the system's electrical equipment, and leaves appropriate margins and sets reasonable safety protection thresholds. The cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms, which has a 2.5 times safety rate compared to the ventricular fibrillation current of 100mA human body current for 500ms. The instantaneous leakage current safety protection current is set to 25mA (maximum can be set to 50mA), and the instantaneous leakage current safety protection duration is set to 150ms, which has a 12 times safety rate compared to the ventricular fibrillation current of 50mA human body current for 1s.

[0024] (3) Leakage current detection logic flow judgment.

[0025] Cumulative leakage current protection protects against the total leakage current value, while instantaneous leakage current protection protects against the change in leakage current ΔI. These two protection mechanisms ensure safe and reliable electricity use. When a single sample value of the current leakage current is detected to be greater than the cumulative leakage current safety protection current of 100mA, the filtering timer starts. During the filtering timer, the single sample value is continuously sampled in the form of a sliding window. If each single sample value is greater than the cumulative leakage current safety protection current of 100mA during the filtering timer reaching the cumulative leakage current safety protection duration of 200ms, then it is determined to be a cumulative leakage current fault and the output is cut off.

[0026] When the difference ΔI between the current single-sample value of leakage current and the average value of the previous cycle is greater than the instantaneous leakage current safety protection current of 25mA, filtering timing begins. During the filtering timing process, single-sample values ​​are continuously acquired in the form of a sliding window, and the average value of each cycle and the difference ΔI between them are calculated. If, during the filtering timing process, the instantaneous leakage current safety protection duration of 150ms is reached, each difference ΔI is greater than the instantaneous leakage current safety protection current of 25mA, it is recorded as a fault sampling result. Single-sample values ​​are acquired again and the above process is repeated. If three consecutive sampling results are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off. When calculating the difference ΔI for the first time, the average value of the previous cycle is calculated as 0.

[0027] The instantaneous leakage current fault can only be determined if the three sampling results are completely identical (maximum duration 450ms) under the condition that the instantaneous leakage current safety protection threshold is met. This effectively avoids false leakage current protection caused by external interference signals generated on the detection line.

[0028] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for diagnosing AC leakage current faults, characterized in that, include: The vehicle-mounted electrical distribution box samples the leakage current of the live and neutral wires of the AC electrical equipment to the casing through a zero-sequence current transformer, determines the single sample value and the average value of the leakage current, and judges the stability of the average value; and sets the safety protection current and corresponding duration for instantaneous leakage current and cumulative leakage current. The cumulative leakage current detection logic is executed using a single sample value of the leakage current, the cumulative leakage current safety protection current, and the corresponding duration to determine whether it is a cumulative leakage current fault. The cumulative leakage current detection logic is as follows: When the single sample value of the current leakage current is detected to be greater than the cumulative leakage current safety protection current, the filtering timer starts. During the filtering timer, the single sample value is continuously sampled in the form of a sliding window. If each single sample value is greater than the cumulative leakage current safety protection current during the filtering timer until the cumulative leakage current safety protection duration, it is determined to be a cumulative leakage current fault and the output is cut off. The difference between a single sampled value of the leakage current and the average value of the previous cycle, along with the instantaneous leakage current safety protection current and the corresponding duration, is used to execute instantaneous leakage current detection logic to determine whether it is an instantaneous leakage current fault. The instantaneous leakage current detection logic is as follows: When the difference ΔI between the current single sample value of leakage current and the average sample value of the previous cycle is detected to be greater than the instantaneous leakage current safety protection current, the filtering timing starts; during the filtering timing process, the single sample value is continuously acquired in the form of a sliding window, the average sample value of each cycle and the difference ΔI between the two are calculated; If, during the process of the filter timing reaching the instantaneous leakage current safety protection duration, each difference ΔI is greater than the instantaneous leakage current safety protection current, it is recorded as a fault sampling result; the single sampling value is reacquired and the above process is repeated. If three consecutive sampling results are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off simultaneously. When a cumulative leakage current fault or a transient leakage current fault is detected, the vehicle's electrical distribution box automatically cuts off the power input and issues an alarm.

2. The AC leakage current fault diagnosis method according to claim 1, characterized in that, The vehicle is designed with a dedicated grounding copper plate. The mounting rack or cabinet of the AC electrical equipment is connected to the vehicle's dedicated grounding wire. The vehicle's dedicated grounding wire is connected to the grounding copper rod on the grounding copper plate, and the grounding copper rod is inserted into the ground. This allows the leakage current to flow into the ground quickly in the event of a leakage current protection mechanism failure.

3. The AC leakage current fault diagnosis method according to claim 1, characterized in that, The determination of the single sample value and the average sample value of the leakage current is specifically as follows: The leakage current sampling module of the vehicle power distribution box reads the leakage current value collected by the zero-sequence current transformer once every T1 time, and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value. After the sampling module continuously reads the single sample value N1 times in one cycle, it calculates the average value of the current N1 single sample values ​​and compares it with the N1 single sample values. If the difference is less than or equal to the sampling value threshold, the average value is recorded; if there is a difference greater than the sampling value threshold, the average value is not recorded.

4. The AC leakage current fault diagnosis method according to claim 3, characterized in that, T1 is 10ms, N1 is 32 times, and the sampling threshold is 4mA.

5. The AC leakage current fault diagnosis method according to claim 1, characterized in that, A stable average sampling value is the inherent leakage current generated during the design of electrical equipment, excluding leakage current caused by equipment insulation failure.

6. The AC leakage current fault diagnosis method according to claim 1, characterized in that, The cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms; the instantaneous leakage current safety protection current is set to 25mA, and the instantaneous leakage current safety protection duration is set to 150ms.

7. The AC leakage current fault diagnosis method according to claim 1, characterized in that, When calculating the difference ΔI for the first time, the average value of the samples from the previous period is calculated as 0.

8. A terminal device, comprising a processor, a memory, and a computer program stored in the memory; characterized in that, When the processor executes a computer program, it implements the AC leakage current fault diagnosis method according to any one of claims 1-7.

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